To keep the Windows operating system stable and secure, Microsoft constantly updates it. However, any update can cause a software regression—an undesired change in the system's stable parts. A key technique for fighting regressions is thorough testing of all updates, which is costly. A statistical model that estimates the risk for updates on the basis of their characteristics makes testing more efficient. Training this model requires collecting data on a large number of fixes made in previous versions of Windows. The Binary Change Tracer tool gets this information from the disparate data sources.